Panel-shaped fluorescent lamp



July 31, 1962 G. E. lNMAN PANEL-SHAPED FLUORESCENT LAMP 2 Sheets-Sheet 1 Filed Nov. 24, 1959 Fi cl l.

lnvervtor: Ge 011% E. Inman M)? His A t lrofnem July 31, 1962 G. E. INMAN PANEL-SHAPED FLUORESCENT LAMP 2 Sheets-Sheet 2 Filed Nov. 24, 1959 lnveafi tov: Gem" e}. Inm an 10 7*" 8 His Attovne3 nite 3&47363 li atented July 31, 1962 3,947,763 PANELSEB FLUORECENT LAMP George E. Inman, East Cleveland, @hio, assignor to General Electric Company, a corporation of New York Filed Nov. 24, B59, Sser. No. 855,1d8 3 Claims. (Cl. 313l09) The invention relates to low pressure discharge lamps such as fluorescent lamps, and more particularly to panelshaped lamps wherein compactness is achieved by a labyrinthine discharge path between the electrodes, for instance a sinuous, zigzag or spiral path.

Lamps of this type have been proposed heretofore wherein the discharge path is a channel formed between two vitreous components sealed together, one or both of the components having upstanding ridges which separate adacent parts of the discharge path from one another. The length of the discharge path is one of the principal factors in determining the light output and the luminous efliciency of a lamp, the longer the lamp the greater the output and efficiency. Therefore such panelshaped lamps otter substantial advantages where compactness of the source and ease of handling are desired, as for instance in domestic lighting and lighting of restricted spaces such as closets and hallways.

It is well-known that in low pressure positive column lamps wherein phosphors are excited by the resonance radiation of mercury, it is possible to obtain either improved efliciency of operation or greater current capacity and discharge wattage when the discharge is constricted out of round. This may be done by providing an oval or flattened cross section or again a kidney-shaped cross section as is done in some lamps marketed by applicants assignee and now well-known under the designation Power Groove. It would be desirable to achieve in a panel-shaped discharge or fluorescent lamp, some of the advantages which follow from a constricted or non-circular cross section in the discharge channel.

Therefore the general object of the present invention is to provide an improved panel-shaped discharge lamp structure which achieves some of the advantages of a constricted or noncircular discharge channel.

Another object of the invention is to provide a panelshaped discharge or fluorescent lamp which achieves plasma constriction in a vitreous envelope without requiring excessive wall thickness whereby to maintain weight and manufacturing cost within practical bounds.

It is known that fluorescent lamps which depend upon the generation of mercury resonance radiation of 2537 A. have an optimum mercury vapor pressure in the vicinity of 6 microns for maximum light output or efficiency. This is generally achieved by providing that the lamp envelope or at least a part of it is at a temperature corresponding to this optimum vapor pressure, about 40 C. Panel-shaped fluorescent lamps, by reason of the very compactness which is their most attractive trait, are at a disadvantage in this respect. Therefore a further object of the invention is to provide a panel-shaped discharge or fluorescent lamp, preferably fulfilling the requirements of the objects recited earlier, and in addition having a configuration such that optimum mercury vapor pressure control is readily effected.

The invention attains its objects by providing in a panel-shaped or labyrinth discharge lamp a discharge space or channel extending substantially throughout the panel and having a cross section which is flattened or compressed out of round with the major or longer dimension of the cross section transverse or perpendicular to the plane or web of the lamp. In one form, the cross section may be ov-al or elliptical with the major axis of the oval transverse to the web of the panel which occurs near the middle of the long sides of the oval. This configuration achieves simultaneously the desired increase in efficiency or loading capacity due to the noncircular cross section, and improved rigidity and resistance to implosion. At the same time it provides the desired cool regions near the lower edge of the discharge channel for the maintenance of optimum mercury vapor pressure. In another form of the invention, a nonsymmetrical discharge channel cross section may be used wherein the web is located either at or close to the upper edge of the lamp resulting in a somewhat wedge-shaped constricted cross section.

In the drawings accompanying and forming part of the specification, and wherein like reference numerals denote corresponding parts in the several views:

FIG. 1 is a plan view of a rectangular panel-shaped or labyrinth fluorescent lamp embodying the invention.

FIG. 2 is across sectional view of the lamp of FIG. 1.

FIG. 3 is a cross sectional view of a variant of the invention relative to the lamp of FIG. 1.

FIG. 4 is a plan view of a circular panel or labyrinth lamp likewise embodying the invention.

FIG. 5 is a cross sectional view of the lamp of FIG. 4.

Referring to FIGS. 1 and 2 of the drawing, the envelope 1 of the lamp is in the form of a generally flat rectangular panel made up of a pair of light-transmitting complementary molded glass components 2, 3. The glass components are molded or blown to define cooperatively a labyrinthine discharge channel or passage by means of four parallel ridged sections 4 extending side by side and joined by curved end sections 5. The components are fusion-sealed together at least at th peripheral junctures 6 along their outer edges, either directly by fusion of the glass, or through the use of a lower melting point soldering glass, to form a hermetically sealed device. Along the intermediate junctures 7 where the glass components revert and abut together in order to define the labyrinthine channel, they are likewise preferably fusion-sealed together in order to achieve maximum strength. However fusion sealing is not essential along the intermediate junctures 7 provided they fit closely together because under these circumstances the discharge will not leak through but will follow the labyrinthine path. Also when the envelope is evacuated, the components are pressed together by atmospheric pressure so that the assembly is rigidified despite lack of sealing of the intermediate junctures.

In accordance with the invention, the glass components 2, 3 define a discharge channel which is flattened or constricted out of round transversely to the plane of the lamp, that is transversely to the plane of the web formed by the junctures 6, 7 of the components. Thu as illustrated in FIG. 2, the discharge cross section is generally oval or elliptic with the major dimension a normal to the plane of the web, and the minor dimension b parallel to the plane of the web. The flattening of the discharge cross section in a resonance radiation lamp, for instance a low pressure mercury vapor or sodium vapor lamp, as a means to improve the efficiency at a given loading by increasing the ratio of perimeter to area of the cross section is well-known and is discussed for instance in Patent 2,482,421, Lemmers, Flat Tube Electrical Device. Among the factors which are believed to be responsible for the increase in efficiency or loading capacity are the reduction in the reabsorption of resonance radiation and the increase in wall losses resulting in a higher electron velocity or temperature. The degree of flattening may be defined as the ratio a/ b where a is the major dimension of the oval or ellipse and b is the minor dimension. In general, flattening in a ratio of 2:1 or better otters real advantages from the point of View of increased efficiency or loading capacity. In the lamp illustrated in FIGS. 1 and 2 of the drawing, the degree of ace-mes izlasttelning, as given by the ratio a/ b, is approximately In addition to achieving the desired increase in efliciency or loading capacity, flattening of the discharge channel so that the major dimension of the oval is transverse to the plane of the lamp simultaneously achieves the desired rigidity and implosion resistance. This is believed to be due to the fact that the Web portions of the panel, that is the flat junctures 6, 7 are located about at the center of the long sides of the oval. If it were not for the web portion 6, 7, this is where the lamp would be weakest and most subject to inward collapse due to atmospheric pressure. The presence of the web portion 6, 7 provides the necessary rigidity in this region. As a result, the lamp envelope may be made of relatively thin glass panels, thus achieving an economical lamp which is relatively light in weight. The lamp is provided with a pair of discharge supportmg electrodes 8, 9 sealed through the upper component about at the ends of the laybrinthine channel. The

emitting portion proper of each electrode may consist of a coiled-coil filament 10 of tungsten wire provided with an overwind and coated with alkaline earth electron emitting oxide. The filament is supported across a pair of inleads ll sealed through a mount 12 and connected to external base pins or terminals 13. If desired, the electrodes may be of the low resistance low thermal capacity rapid start type disclosed and claimed in US. Patent 2,774,918, Lemmers, Electric Discharge Device, assigned to the same assignee as the present invention. In the larger sizes of lamp an intermediate electrode 14 may be provided to facilitate starting on low voltage; the intermediate electrode is placed so as to be about midway along the laybrinthine discharge channel between the main or end electrode 8, 9.

The lamp contains an ionizable atmosphere including a starting gas or mixture of one or more of the inert rare gases of group of the periodic table at a low pressure, for instance argon at a pressure of 0.5 to millimeters of mercury, along with mercury vapor. The droplets of mercury indicated at 15 (FIG. 2) exceed in amount the quantity vaporized during operation of the lamp wherein the mercury vapor exerts a partial pressure generally in the range of 5 to 8 microns for optimum generation of 2537 A. radiation. The phosphor coating indicated at 16 on the inside of the envelope converts the 2537 A. resonance radiation into visible light and may be applied either before or after the components 2 and 3 are united and sealed together.

An unexpected advantage resulting from flattening the discharge channel in a panel-shaped lamp so that the major dimension of the oval is transverse to the plane of the lamp in accordance with the invention is the improved control of mercury vapor pressure which results. It is known of course that optimum generation of 2537 A. resonance radiation occurs when the mercury vapor pressure is about 6 microns, corresponding to a temperature of about C. The mercury vapor pressure is determined generally by the coolest portion of the envelope. Thus it is not necessary that the entire envelope be at a temperature of 40 C. and it suifices that a portion thereof be maintained at this temperature in order to serve as a mercury vapor pressure control center. The panel-shaped or labyrinthine lamp is relatively compact by comparison with the usual elongated fluorescent discharge lamp and as a result tends to run too hot. With a flattened discharge cross section, the plasma does not extend in full intensity to the outermost ends of the oval indicated at 17 and 18 in FIG. 2, so that these regions naturally tend to run somewhat cooler. Furthermore by providing the major dimension of the oval transverse to the plane of the lamp in accordance with the invention, a substantial additional cooling effect occurs at the bottom of the oval in the outer branches of the labyrinthine channel, indicated at 18a in FIG. 2. This additional cooling effect is due to the convection flow of air around the lamp when it is horizontally suspended, as from a ceiling fixture. As a result, the mercury condenses almost entirely in the lower portion of the outer branc..es of the labyrinthine channel as indicated at 15, and these portions of the lamp which are at a lower temperature serve as mercury vapor pressure control centers.

FIG. 3 illustrates a variant of the invention in connection with a rectangualr panel-shaped lamp such as that of PEG. 1. In this embodiment, the lamp 21 is formed by means of a generally flat upper component 22 and a molded lower component 23, the two components being peripherally sealed together at 24. The lower component has a cross section which may be described generally as wavy or deeply corrugated and in cooperation with the upper component, defines a flattened or constricted plasma channel which may be described as wedgehaped. With this lamp configuration, the components are preferably sealed together at the intermediate unctures 25 in order to achieve the desired strength and implosion resistance. The transverse dimension a is made substantially greater than the parallel dimension b to achieve the desired constrictive effect, and the improved cooling etfect is likewise obtained at 18a along the lower edge of the outer branches.

FIGS. 4 and 5 illustrate another embodiment of the invention wherein the lamp '39 is made up of a pair of generally circular or disk-like, light-transmitting complementary molded glass components 31, 32 which are fusion-sealed together at their outer and inner peripheries 33, 34. A tortuous discharge channel is defined in the envelope by means of cooperating concentric ridges. The inside ridges 35, 36 on each side of the medial line extend through less than and revert upon themselves. The outside ridge 37 extends substantially the Whole way around the envelope and joins the inside ridges to complete a continuous passage or channel.

in accordance with the invention, the discharge passage or channel is flattened or compressed to a generally oval cross section as shown in FIG. 5, with the major dimension a transverse, and the minor dimension [7 parallel to the plane or Web of the lamp. The intermediate junctures which abut together at 38 are preferably fusionsealed together for maximum strength. The configuration in accordance with the invention achieves the desired constriction of the dicharge for improved efficiency or loading capacity and its particular disposition along with the location of the web portions assures maximum strength and resistance to implosion. This configuration also achieves improved mercury vapor pressure control through the lower portion 37a of the outermost ridge 37. This portion is most efl ectively cooled by convection flow of air during operation of the lamp so that excess mercury 15 condenses therein, and its temperature determines the mercury vapor pressure throughout the lamp.

The circular form of panel or labyrinth lamp illustrated in FEGS. 4 and 5 is also adaptable to the variant in cross section illustrated in FIG. 3 wherein only the lower vitreous component is ridged to provide the plasma channel and the upper component is substantially flat. An auxiliary electrode 14 may be provided in addition to the main electrodes 8, 9 in order to facilitate starting. This auxiliary electrode is preferably located at the midpoint of the outer ridge 37 so as to be located midway along the discharge channel between the main electrodes. If desired the upper component 31 may have an internal light reflecting layer 39, for instance of titanium dioxide, interposed between phosphor layer 16 and the glass wall so as to direct downward the major portion of the light produced by the lamp.

The specific embodiments of the invention which have been illustrated and described in detail are intended as exemplary and not as limitative of the invention whose scope is to be determined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An envelope for an electric discharge lamp comprising a pair of vitreous plate-like components sealed together along their margins, said components being cooperatively ridged to provide a labyrinthine discharge path between the components and extending substantially throughout the area of said components, one of said components being much more deeply ridged than the other whereby the cross section of said discharge path is compressed out of round and generally oval shaped with a major dimension transverse to the principal plane of said components and a minor dimension parallel to said plane, and the ratio of said major to said minor dimension being at least two to one.

2. An electric discharge lamp comprising a pair of plate-like vitreous components sealed together along their margins, one of said components being substantially flat and the other being deeply ridged to provide a labyrinthine discharge channel therebetween extending substantially throughout the area of said lamp, the cross section of said dis-charge channel being constricted out of round and having a major dimension transverse to the principal plane of said lamp and a minor dimension parallel thereto, the ratio of said major to said minor dimension being at least two to one, a pair of electrodes sealed into opposite ends of said channel, a filling of an inert gas and mercury within said channel, and a coating of phoshor on at least a portion of the inside surface thereof of said channel.

3. An electric discharge lamp comprising a pair of plate-like vitreous components sealed together along their margins, one of said components being substantially fiat and the other being deeply ridged to provide a labyrinthine discharge channel therebetween extending substantially throughout the entire area of said lamp, said discharge channel being constricted out of round and having a major dimension transverse to the principal plane of said lamp and a minor dimension parallel thereto, said major dimension being substantially greater than said minor dimension by a ratio of at least two to one, a pair of electrodes sealed into opposite ends of said channel, a filling of an inert gas and mercury within said channel, a coating of a phosphor on at least a portion of the inside surface thereof, said components having junctures abutting together between the ridged portions which rigidify the envelope and improve its resistance to implosion, and the lower ridged portions serving as mercury vapor pressure control centers.

References Cited in the file of this patent UNITED STATES PATENTS 1,984,215 Hotchner Dec. 11, 1934 2,255,431 Marden et al. Sept. 9, 1941 2,555,749 Krefft June 5, 1951 2,643,020 Dalton June 23, 1953 FOREIGN PATENTS 959,678 France Apr. 3, 1950 

